In my experience, the DoL and Immigration don't have/want much contact with each other. Out of policy, rather than law, immigration advise foreigners to change their retirement to a non-B. I can't think of any real reason why someone would be opposed to this, apart from when they leave the job, they might have some issues as the non-B is linked to the work permit.
Isn't an extension based on retirement a 'non immigrant visa'?
I agree, I can't find anything in the law that states otherwise.